The environment for the present invention is disclosed in issued U.S. Pat. No. 4,615,273 entitled "Conveyorized Transport System" and a typical prior art escapement mechanism is shown in U.S. Pat. No. 4,667,602 entitled "Escapement Mechanism". Another related disclosure is contained in Ser. No. 249,442, filed Sept. 6, 1988. These disclosures describe the environment for the present invention and are incorporated by reference herein.
Workpiece conveyor systems of the type with which this invention is particularly suited may, for example, be used in a garment making plant to carry pieces, selectively, into and through a series of work stations provided alongside a main conveyor. Without a conveyor system of this type the garment workers not only perform the work operations provided at the various work stations, but additional workers must be assigned to; punch labels that are in turn attached to each workpiece to make a record of its status; sort the workpieces; and transport them usually manually to and from several such work stations. The number of steps involved leads to a labor intensive plant and creates other problems in the assembly process. For example, the time it takes a worker to perform various tasks is generally unpredictable and difficult for supervisory personnel to keep track of. Also, it can be difficult to keep track of the workpieces and of the time required for these pieces to travel to and from the various work stations. In order to provide a more accurate scheduling of such work it is commonplace for workers to accumulate many workpieces before carrying them to a subsequent work station. As a result considerable inventory may be tied up in the garment plant introducing excessive costs to the manufacturer. Further, accumulating workpieces in such piles tends to make accurately updated quality control inspections more difficult to accomplish.
As disclosed in the above mentioned U.S. Pat. No. 4,615,273 a conveyorized transport system provides a main rail upon which workpiece trolleys ride, and closed subsidiary work station loops located alongside this main rail. Each such loop leads to and from an individual work station. Switching means is provided for each such subsidiary loop for transferring trolleys between the main rail and such subsidiary loops. These loops each have an entrance and an exit end, the entrance end being adjacent to the exit end relative to the general direction of trolley movement on the main rail or track of the conveyor system. This transfer switch is able to deliver a trolley to the entrance and to receive a trolley from the exit of each loop. The configuration of each loop provides flexibility in routing because it allows trolleys to be routed in two or more ways from an exit of a subsidiary loop. The main rail and subsidiary loop each have a gap and a transfer switch is provided to shunt trolleys therebetween. Such a switch comprises a rail section that can be moved during switching from a first position bridging a gap in the main rail to a second position aligned with the entrance end of the subsidiary loop to provide for transfer of the trolley from the main rail to the subsidiary loop. This type of switch also allows the trolley to be routed from one subsidiary loop to another located directly across the main rail, or vice versa, or from a discharge or exit end of the subsidiary loop directly to the entrance of the same subsidiary loop for recirculation.
The prior art disclosures referred to above teach that each closed subsidiary loop comprises an inclined gravity rail for feeding the trolleys to and through a work station, with an elevator means provided for lifting the trolleys from the lower end of the gravity rail to (a point and to a level) position where the trolleys can be reloaded on the main conveyor rail.
The primary aim of the present invention is to provide an improved escapement means between the work station and the elevator means for accumulating trolleys on the gravity rail and for accelerating the trolleys individually into the elevator means or into a transfer slide assembly such as shown in the application referred to above, and filed Sept. 26, 1988 under Ser. No. 249,442.